1. Field of the Invention:
The invention relates to an apparatus for the formation of images utilizing electrophotography, which comprises process-cartridges detachably mounted in the body of the apparatus, each of the said cartridges integrally housing process-units for carrying out each process of the electrophotography.
2. Description of the prior art:
In recent years, an apparatus for the formation of images such as a copying apparatus, a laser printer, or the like, in which a process-cartridge integrally comprising process-units such as a photosensitive drum, a charger, a cleaning device, a developing device, a toner storage container, a used toner collecting container, and the like, is detachably mounted in the body of the apparatus, has been put into practical use. Such an apparatus comprising one process-cartridge is advantageous in that a variety of work for the maintenance of the apparatus, such as toner resupply, disposal of used toner, replacement of the photosensitive drum or other process-units, and the like, can all be done at the same time by anyone just by replacing one process-cartridge with a new one, while this kind of work can be done only by a specialist in the case of an apparatus having no process-cartridge.
In such an apparatus, the single process-cartridge includes all process-units as described above but these process-units usually differ in lifetime. Thus, when the lifetime of one of the process-units expires, all of them are replaced with new ones in the single process-cartridge. In this way, all the other process-units which can still be used are also discarded. This causes a high cost of the maintenance for the whole apparatus.
Japanese Laid-Open Patent Publication No. 62-32483 discloses an apparatus for the formation of images for the purpose of overcoming this problem. This apparatus comprises two process-cartridges, which are detachably mounted in the body of the apparatus. One is a photosensitive cartridge including a photosensitive means and its peripheral devices such as a cleaning device and the like. The other is a developing cartridge which includes devices related to the developing process such as a developing device, a toner storage container, and the like. The lifetime of the photosensitive cartridge expires at the time when about 5,000-20,000 sheets of copy paper are printed with use of the whole apparatus. The lifetime of the developing cartridge, which depends on the volume of developer stored in the toner storage container, expires at the time when about 500-5,000 sheets are printed with use of the whole apparatus. Thus, when the lifetime of one cartridge expires, it can be separately replaced with a new one, with the other cartridge still kept within the body, so that each cartridge can be used until its lifetime expires, resulting in relatively improved economy in the maintenance of the whole apparatus.
Moreover, this apparatus is provided with a means for transporting used toner collected by the cleaning device of the photosensitive cartridge into the developing cartridge. Thus, a used toner collecting container for keeping the used toner therein need not be disposed within the photosensitive cartridge and can be disposed within the developing cartridge instead. The lifetime of the photosensitive drum and its peripheral devices within the photosensitive cartridge is far longer than that of the used toner collecting container. If the used toner collecting container is disposed in the photosensitive cartridge, it must be made remarkably large so as to have a lifetime equivalent to that of the photosensitive drum and its peripheral devices, resulting in a photosensitive cartridge of a remarkably large size. This will prevent the whole apparatus from being miniaturized. On the other hand, with this apparatus in which the used toner collecting container is not disposed in the photosensitive cartridge but disposed in the developing cartridge, the used toner collecting container need not be made so large since the lifetime of the process-units in the developing cartridge is not so long as that of the photosensitive cartridge. This enables the miniaturization of the whole apparatus.
In such an apparatus comprising two process-cartridges, although the process-units in the photosensitive cartridge do not differ in lifetime to a great degree and thus can be fully used until their lifetime expires, the developing cartridge still has problems as will be described below.
The developing cartridge of the apparatus integrally comprises a developing device, a toner storage container, and a used toner collecting container. Thus, even when the lifetime of only one of them expires, all of these three process-units should be replaced with new ones as one developing cartridge. The maximum number of copy sheets that can be printed with use of the developing device depends on the kinds of developer. When one-component developer is used, the maximum number of sheets that can be printed with use of the developing device is nearly infinite. When two-component developer is used, the maximum number is about 10,000. In general, the toner storage container has a volume for toner with which a maximum of about 500-5,000 of copy sheets can be printed. The lifetime of the used toner container is substantially as long as that of the toner storage container. Thus, the lifetime of the developing device is far longer than that of these two containers; even when the two-component developer is used, the lifetime of the former is twice as long as that of the latter. As described above, the two containers and the developing device should be replaced with new ones together as one cartridge. Thus, when the lifetime of the containers expires first, the developing device which can still be used for a long time should also be discarded together with them. This causes an increased cost of maintenance of the whole apparatus. On the other hand, if the lifetime of the two containers is set to be equivalent to that of the developing device utilizing the twocomponent developer, the above problem of the high maintenance cost may be solved, but the toner storage container and the used toner collecting container must be doubled in size. This will prevent the whole apparatus from being miniaturized.